class Solution {
public:
    int longestPalindromeSubseq(string s) {
        int n = s.size();
        vector<vector<int>> dp(n,vector<int>(n,1));//初始化为1，表示i==j的时候一个字符长度的回文串
        for(int i=n-1;i>=0;i--)
        {
            for(int j=i+1;j<n;j++)//从i后面进行枚举
            {
                if(i+1==j &&s[i]==s[j])
                    dp[i][j] = 2;
                else if(s[i]==s[j])//长度大于2
                {
                    dp[i][j] = dp[i+1][j-1]+2;
                }
                else
                {
                    dp[i][j] = max(dp[i][j-1],dp[i+1][j]);
                }
            }
        }
        return dp[0][n-1];
    }
};